Switched Reluctance (SR) electric machines such as, for example, motors and generators may be used to generate mechanical power in response to an electrical input or to generate electrical power in response to a mechanical input. Magnetic, resistive, and mechanical losses within the motors and generators during mechanical and electrical power generation cause a build up of heat, which may be dissipated to avoid malfunction and/or failure of the device. One of the limitations on the power output of the electric generators may be the capacity to dissipate this heat.
One example of a liquid cooled generator is depicted in FIG. 7. The generator 300 generally includes a rotor assembly 302 including a rotor shaft 304 with steel laminations 306. Surrounding the rotor assembly 302 is stator assembly 308, which includes a plurality of stator coils 310. Rotor 302 is configured for rotation about axis 312 within stator 308 for generation of electrical power in a conventional manner.
The stator 308 and rotor 302 are disposed within a cavity 314 defined by a generator housing including a front housing 316, middle housing 318, and rear housing 320, with middle housing 318 including an inner surface 322. Fitted against inner surface 322 is a cooling sleeve 324 having a series of grooves 326 forming a cooling passage when outer surface 327 of sleeve 324 is mated against inner surface 322. O-rings 328 are positioned in the sleeve surrounding the grooves 326 to prevent leakage of coolant. The sleeve includes a radially extending flange 330 being positioned between front housing 316 and middle housing 318. An upper axial lubricant/cooling bore 340 passes through the front housing 316, flange 330, middle housing 318, and rear housing 320, sealed by O-rings 334. Similarly, a lower lubricant/cooling sump 336 is sealed by O-rings 338 between the flange 330, front 316, and middle 318 housings.
One method of dissipating heat within a generator includes a fluid cooled electric device having outer and inner surfaces that define a housing cavity having a longitudinal axis with a helical conduit integrated within the housing between the outer and inner surfaces thereof, along the axis. U.S. patent application Ser. No. 11/975,612 (the '612 application) to Savant teaches such a liquid cooled switched reluctance electric machine that includes a helical conduit integrated within the housing between the outer and inner surfaces thereof, along the axis.
However, coring a continuous internal helical cooling conduit is a challenge, from both technical and cost standpoints. One major factor is the inherent springiness of the conduit, due to its spiral geometry. As a result, the core may shift in diameter and length resulting in casting rejects. Core flex may also occur when sand is poured or compacted in the mold, leading to inconsistency between any two castings. Also, the thermal forces generated during the solidification process may cause the core to compress axially, requiring access holes to clean sand from the cored cooling grooves after the housing is cast. Additionally, the cost associated with the tooling required for coring a continuous helical conduit may be prohibitive.
The disclosed method is directed to overcoming one or more of the challenges set forth above.